Granite and marble are considered to be highly desirable architectural materials for forming the exterior facade or facing of building structures, such as a skyscraper. These materials are not only highly pleasing in appearance, but also very durable and require only a minimum of maintainance. This is borne out by the many marble or granite faced buildings throughout the world which were constructed hundreds of years ago and are still in use today. However, the scarcity of marble relative to the current demand and the unprecedented rise in the cost of construction labor has drastically increased the cost of constructing buildings faced with marble or granite.
In an early construction method, still used today, selected pieces of facing material of marble or granite were hand set directly on the structural steel skeleton or concrete frame of a building. The panels were held in place by bolts or similar hardware. In this type of construction, the panels of the stone facing material must be at least several inches thick to have the strength necessary to support their own weight without cracking. These thick panels are not only very costly to quarry and cut to size, but also are difficult to handle if made in a desirably large size to cover a building surface at a reasonable rate. If the height and width of the panels are decreased to make them easier to handle, an increased number of panels are needed to cover the building surface thereby increasing the number of time-consuming panel mounting operations required.
Once the marble or granite facade has been attached to the steel or concrete frame or backing, a separate interior wall must be erected. Modern fire codes for commercial structures typically prohibit the use of flame-transmitting materials in the construction of the building walls. In addition, building codes now require that exterior walls be insulated to minimize heat loss in the winter and heat gain in the summer.
Other methods of attaching a granite or marble facing material to a building include that shown in U.S. Pat. No. 3,299,601, wherein C-shaped clips are inserted within openings drilled in the rear surface of marble slabs. Thereafter, a layer of dense cementatious material is spread over the rear faces of the slabs. Before the cementatious layer sets up, a sheet of wire mesh and a frame composed of a metallic corrugation surrounded by channel members are placed over the dense cementatious material. Next, a porous cementatious, second layer is applied over the first dense layer and around the corrugations to completely fill the envelope defined by the corrugations and the surrounding channel members. One drawback of this particular construction is that because the space between the corrugations is entirely filled with cementatious material, insulating material, such as rock wool or glass fiber, must be placed behind the wall panel resulting in a relatively thick structure. Moreover, a separate inside wall must be provided.
A further method of attaching a granite or marble facing to a building is disclosed by U.S. Pat. No. 3,724,152, which includes backing the selected architectural grade facing material with a supporting member of suitable hard stone, such as marble or granite, and then backing this hard stone with a layer of conventional concrete. The facing material, backing stone and concrete are then attached to the building structure by suitable fasteners, such as bolts. In this method, although relatively thin panels of facing material were used, the stone and concrete backing is required to provide sufficient structural integrity to mount the facing material without cracking.
U.S. Pat. No. 4,223,502 concerns a building wall panel adapted to be mounted on a building structure to form at least a portion of the outer walls of the structure. The building panel includes a plurality of granite or marble panels with pairs of holes drilled in their rear sides for receiving C-shaped anchor clips. A layer of glass fiber reinforced concrete is sprayed over the back surfaces of the granite or marble panels and around the anchor clips to connect the panels to the concrete backing layer. A drawback of this particular construction is that the wall panel only serves as an exterior facade for the building thereby necessitating a separate inner wall structure which also must be attached to the building frame. Moreover, building panels constructed in this manner are limited to a maximum length of approximately fifteen feet. To reduce building costs, it is desirable that structural panels be substantially larger in size, for instance in the range of thirty feet in length or more.
French Pat. No. 2,304,742 discloses a prefabricated building wall unit composed of ceramic panels or blocks which are set within a backing layer of cement mortar reinforced with fiberglass. As in the above-discussed U.S. Pat. No. 4,223,502 patent, there is a limitation as to the maximum size in which this type of building unit may be made and still safely support the ceramic blocks.
A wall panel having finished plaster surfaces on both sides is shown by U.S. Pat. No. 2,241,338 as including a facing of plasterboard or gypsum board secured to one side of a frame formed from a plurality of metal studs. A layer of plaster overlays the plasterboard on both sides of the frame. The disclosed structure is not well adapted to prefabrication as the plasterboard is attached to the metal frame after the metal frame is secured within a building. In addition, the layers of plaster are applied to the plasterboard after the partition is in place, thereby requiring time-consuming, on sight fabrication to produce the finished partition.
U.S. Pat. No. 3,885,008 discloses a wall section composed of an external, molded panel bonded to a wooden frame. The external wooden panel is formed from comminuted earthen and plastic materials and is attached to the wooden frame by overlying the entire back surface of the molded panel and the sides of adjacent wooden frame members with a layer of fiberglass reinforced plastic. This wall panel has inherent structural as well as durability limitations. For example, the external molded plastic panel is subject to cracking and separation from the underlying wooden frame when exposed to the tensile and twisting forces occuring in a multi-story structure. In addition, the inherent structural weakness of the underlying wooden frame generally prohibits prefabricating a wall panel into a single, large multi-story unit. Also, the plastic exterior molded panel, the bonding compound securing the molded panel to the wooded frame, and the wooden frame itself are all flamable materials which would not satisfy fire codes for commercial structures.
U.S. Pat. No. 4,185,437 discloses a building wall panel having an exterior facing of fiberglass reinforced concrete bonded to a support frame formed by metal channel members which are arranged so that their flanges lie against the back side of the exterior facing. A second layer of fiberglass reinforced concrete is applied to both a portion of the rear surface of the exterior facing and the flanges of the channel members at intervals along each channel member.
Accordingly it is a principal object of the present invention to provide large, unitary building wall panels which are faced with thin panels of granite and marble, constitute both the exterior and interior walls of the building, and meet existing fire and insulation codes for commercial structures, thereby overcoming the limitations of the known building wall panels discussed above.